Problem: Solve for $x$ and $y$ using substitution. ${-2x-3y = 10}$ ${x = -2y-9}$
Explanation: Since $x$ has already been solved for, substitute $-2y-9$ for $x$ in the first equation. ${-2}{(-2y-9)}{- 3y = 10}$ Simplify and solve for $y$ $4y+18 - 3y = 10$ $y+18 = 10$ $y+18{-18} = 10{-18}$ ${y = -8}$ Now that you know ${y = -8}$ , plug it back into $\thinspace {x = -2y-9}\thinspace$ to find $x$ ${x = -2}{(-8)}{ - 9}$ $x = 16 - 9$ ${x = 7}$ You can also plug ${y = -8}$ into $\thinspace {-2x-3y = 10}\thinspace$ and get the same answer for $x$ : ${-2x - 3}{(-8)}{= 10}$ ${x = 7}$